Ask Hamish: how to choose the right glass cloth for your project

Choosing the right glass cloth is the starting point for any successful boatbuilding or repair project. Make the right choice with our four key selection criteria says technical expert, Hamish Cook.

Plain weave, biaxial stitched, twill weave, satin weave. The range of glass cloths available is huge and growing. So how can you make sure that you choose the right one?

The simple answer is to consider the function your glass cloth needs to fulfil. Does it need to strengthen a joint or transfer a load between two components? Does it have to be thin and light? Does it have to drape easily over curved components? Or does it need to look great under a clear finish?

Here are our four key selection criteria to help you choose the right cloth for your project:

StrengthIf you need to transfer a load across a joint, it’s likely that a stitched biaxial cloth will be the right choice for you. With woven fabrics, 50% of fibres run in parallel to your joint, which means they’re doing nothing to strengthen it. In contrast, stitched biaxial fabrics use 100% of fibres to transfer load between components, making your joint much stronger.

This means biaxial cloth is great for applications such as bulkhead installation or repairs to glass tabbing. You can be sure that the weight you’re adding to your boat in terms of glass cloth and epoxy is delivering the best results in terms of structural strength and resilience.

WeightSmall boats such as dinghies need to be extremely light. For this reason, many small boatbuilding projects, including many stitch and glue construction projects, recommend plain weave glass cloth. With plain weave, you still get 50% of fibres working for you to strengthen joints, which is often enough for lighter boats. There is also the option to use a twill weave, which reduces crimping to provide stronger laminates that are still relatively light.

For larger boats, where strength rather than weight is the primary consideration, many naval architects recommend stitched biaxial cloths. In all cases, stitch and glue kits all come with recommendations for glass cloths that provide the right balance of weight and structural strength.

DrapabilityFor some applications, we need fabric that will drape easily over curved surfaces, such as the hull of a small, cedar-stripped canoe, for example. For this, we use satin weave fabrics that use offset weaves (one under, two over or similar). Draping fabric over curved surfaces is much more difficult with plain weave fabrics and impossible with stitched biaxial fabrics that are much more rigid.

FinishWhen choosing your cloth, you need to think about the kind of finish you want to achieve. If you want a clear, varnished, finish you’ll need to use a woven cloth that will flow out nicely when wetted out with epoxy. Remember that the stitching used in biaxial cloth is generally nylon and can usually be seen even after the cloth is wetted out, so not good for clear finishes.

There are also specialist fabrics available that can help you achieve the finish you want. One example of this is one of our satin weave fabrics that has a tapered edge. This is great for large hulls as it allows you to overlap the tapered edges of the cloth to achieve a perfect finish, with no “high” spots and no visible joins. It’s fantastic for clear coating, painted finishes or anti-foul finishes. It also means there’ll be less work to do in terms of creating a fair surface for varnishing or painting.

For more information about choosing the right glass cloth for your project, download our sheathing guide. You can also watch a video blog on choosing the right materials for your project.